Optimization of the combustion synthesis towards efficient LaMnO3+y catalysts in methane oxidation

The present work deals with the synthesis and the study of physico-chemical and catalytic properties of a series of lanthanum manganite perovskite-type oxide using the one-step combustion method. Glycine was used as complexing agent and fuel. Seven glycine-to-nitrate ratios from 0.32 to 0.8 were investigated. XRD patterns show a single phase perovskite type oxide when glycine-to-nitrate ratio is above 0.37. Glycine/nitrate ratio affects significantly the surface areas, which range in 18–37 m2/g. The use of fuel-rich precursor allows an enhancement of the specific surface area, the reducibility of manganese and the mobility of desorbed oxygen. The light-off temperature for 50% and 90% of methane conversion was found to be directly related to surface areas. The highest catalytic activity was obtained for glycine-to-nitrate ratio of 0.8, which exhibits the highest superficial concentration of manganese and the highest amount of active oxygen. This catalyst shows also a good thermal stability.

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► LaMnO3 synthesized by combustion method with different glycine/nitrate ratios.
► Their catalytic activity in CH4 oxidation directly related to the specific area.
► Higher catalytic performances for glycine-rich precursors.
► Among the pertinent parameters (Mn4+ concentration, oxygen mobility, crystallite size and SSA), which can account for the proposed mechanisms, the SSA appears to be the most relevant.